The alarm industry provides protection for billions of dollars worth of property and is growing at a rapid rate each year. Typical alarm services provided to the public include burglar alarms, automatic and manual fire alarms, sprinkler system supervision and industrial process supervision.
A significant number of alarm services utilize telecommunications facilities to communicate bidirectional signals between an alarm loop and a remote alarm receiver. The alarm loop comprises one or more alarm transmitters. In general, the telecommunications facilities employed are metallic loops and trunks, i.e., facilities which do not multiplex signals but merely conduct the signals as supplied by an alarm transmitter or alarm receiver. These metallic facilities often extend up to 90 miles. While metallic facilities are highly reliable, their usage presents several problems. First, the number of available wire pairs is becoming increasingly scarce due to the widespread deployment of digital facilities, such as the T-carrier systems. Second, the cost of installing and maintaining long lengths of metallic facilities is very expensive. To overcome these problems, prior art systems have been developed which code and multiplex alarm transmitter signals over digital carrier systems. Such systems, however, are quite expensive and do not provide bidirectional communications capability between the alarm transmitters and the alarm receiver.